Now click on the USB icon on the Pre's notification area, switch to USB Storage mode.

You can now copy the files off of the Pre and edit them any way you want, just make sure they have the same properties as the orig (transparency, size, file extention, etc). I didn't create these image below, they are just edited from the Palm Pre. You can use any 360 x 420 PNG to achieve these results.

Once they are edit to your liking, copy the files back to the Pre in USB mode with the same file name.

Eject your Pre from your computer, wait for Wifi to log back into your network, and SSH into the Pre again. Your old window probably timed out by now so you can close it.

Step 4 (Last)
Now we'll need to get the files (all 3 if you edited them) back to the correct location, so we'll use the copy (cp) command to do this.